1. Field of the Invention
This invention relates to an engine control system, particular to an internal combustion engine control system, more particularly to a control system for an internal combustion engine that is mounted on a machine such as a walk-behind truck and powers the machine.
2. Description of the Related Art
It is known to mount an internal combustion engine on a machine and power the machine using the engine output after it is lowered in rpm and increased in torque by a variable speed reducer. Japanese Laid-Open Patent Application No. Hei 6(1994)-56398, for example, teaches a cargo carrier equipped with a bed for loading cargo (freight), in which the output of the engine is passed through a variable speed reducer whose output of higher torque is used to drive the driven wheels, and in turn the crawler belts, of the cargo carrier, thereby enabling the cargo carrier to travel. The cargo carrier taught by this reference is of the walk-behind type, i.e., of the type the operator walks behind while operating.
This type of walk-behind truck is generally designed to be operated by an operator who walks behind the truck while manipulating an engine speed regulating lever to input an instruction to regulate engine speed and a vehicle speed regulating lever to input an instruction to regulate vehicle speed as desired.
When the engine speed (i.e., output) is too high or too low relative to the load acting on the crawler belts (for the uphill or downhill slope being traversed), the operator manipulates the engine speed regulating lever to adjust the engine speed to what is thought suitable based on experience. On the other hand, when the operator wants to drive the walk-behind truck at a certain speed, the operator uses the vehicle speed regulating lever to input the desired vehicle speed to a control system installed in the walk-behind truck. In response thereto, the control system regulates the engine speed and reduction ratio of the variable speed reducer so as to adjust the walk-behind truck speed to the desired speed.
Japanese Laid-Open Patent Application No. Hei 7(1995)-197829 teaches a generator driven by an internal combustion engine whose output is converted to high torque by a variable speed reducer. The generator of the second reference can be operated to generate alternating current of a predetermined frequency for a certain period of time by controlling the throttle opening of the engine so that the engine maintains a constant speed (rpm).
The speed of this type of generator is generally controlled to remain constant irrespective of the load acting on the generator, i.e., the magnitude of the load produced by outside equipment connected to the generator. This is undesirable from the viewpoint of engine noise and fuel consumption because the engine is maintained at the predetermined speed even when operating under relatively low load.
To overcome this disadvantage, Japanese Utility Model Publication Hei 3(1991)-7555 teaches a generator in which the engine speed is changed (increased/decreased) in accordance with load. There are also known inverter generators that vary the engine speed in accordance with load.